We describe a weighted absolute difference based deinterlace method and apparatus. The deinterlace method and apparatus uses weighted absolute differences along different directions as means for interpolating pixel data using edge orientation detection. The apparatus includes a memory adapted to store a current and previous fields and predetermined portions of a future field of an input signal. A motion detector is adapted to detect motion between the future and previous fields. An interpolating circuit is adapted to generate a plurality of output pixels using a corresponding plurality of methodologies. And a switch is adapted to select between the plurality of output pixels responsive to the motion detector.
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16. A deinterlace method, comprising:
generating motion, no motion, and film mode signals by analyzing pixels in sub images in current, future, and previous fields;
spatially interpolating pixels in the current field;
spatial-temporally interpolating pixels in the current field with pixels from a previous field;
averaging pixels from the future and previous fields; and
selecting between the spatially interpolated, spatial-temporally, and averaged pixels responsive to the motion, no motion, film mode signals.
24. A deinterlace method, comprising:
detecting motion between a future and previous field sub images;
interpolating output pixels using one of several methodologies responsive to the detecting;
storing predetermined lines from the future field in a line memory;
storing the previous field sub image in a previous field memory; and
storing a current field sub image in a current field memory;
where storing predetermined lines from the future field includes selecting a 3×5 future field sub image;
where storing the previous field sub image includes selecting a 3×5 previous field sub image; and
where storing the current field sub image includes selecting a 4×9 current field sub image.
1. A deinterlace apparatus, comprising:
a memory adapted to store a current and previous fields and predetermined portions of a future field of an input signal;
a motion detector adapted to detect motion between the future and previous fields;
a spatial interpolator adapted to generate spatially interpolated output pixels by spatially interpolating the current field;
a spatial-temporal interpolator adapted to generate temporal-spatially interpolated output pixels by temporal-spatially interpolating the previous field with the current field;
an averaging circuit adapted to generate averaged output pixels by averaging the future and previous fields; and
a switch adapted to select between the spatially interpolated, temporal-spatially interpolated, and averaged output pixels responsive to the motion detector.
25. A deinterlace method, comprising:
detecting motion between a future and previous field sub images;
interpolating output pixels using one of several methodologies responsive to the detecting; and
taking an absolute difference between each pixel in the future field sub image and each pixel in the previous field sub image;
where detecting comprises:
generating a first comparison by comparing the absolute difference to a first predetermined threshold;
generating a second comparison by comparing the absolute difference to a second predetermined threshold;
generating a first count by counting first comparisons exceeding the first predetermined threshold;
generating a second count by counting second comparisons below the second predetermined threshold;
generating a no motion signal by comparing the first count to a third predetermined threshold; and
generating a motion signal by comparing the second count to a fourth predetermined threshold.
11. A deinterlace apparatus, comprising:
a memory adapted to store a current and previous fields and predetermined portions of a future field of an input signal;
a motion detector adapted to detect motion between the future and previous fields;
an interpolating circuit adapted to generate a plurality of output pixels using a corresponding plurality of methodologies; and
a switch adapted to select between the plurality of output pixels responsive to the motion detector;
a spatial interpolator adapted to generate spatially interpolated output pixels by spatially interpolating the current field;
a spatial-temporal interpolator adapted to generate temporal-spatially interpolated output pixels by temporal-spatially interpolating the previous field with the current field;
an averaging circuit adapted to generate averaged output pixels by averaging the future and previous fields;
where the motion detector generates motion, no motion, and film mode signals; and
where the switch selects the spatially interpolated output pixels responsive to the motion signal, the averaged output pixels responsive to the no motion signal, the temporal-spatially interpolated output pixels responsive to the motion and no motion signals, and output pixels from the future field responsive to the film mode signal.
8. A deinterlace apparatus, comprising:
a memory adapted to store a current and previous fields and predetermined portions of a future field of an input signal;
a motion detector adapted to detect motion between the future and previous fields;
an interpolating circuit adapted to generate a plurality of output pixels using a corresponding plurality of methodologies; and
a switch adapted to select between the plurality of output pixels responsive to the motion detector;
where the motion detector comprises:
a subtracting circuit adapted to generate an absolute difference of pixels in the future field from corresponding pixels in the previous field;
a first comparator adapted to generate a first compare signal by comparing the absolute difference to a predetermined first threshold;
a second comparator adapted to generate a second compare signals by comparing the absolute difference to a predetermined second threshold;
a first counter adapted to generate a first counter signal by counting first compare signals;
a second counter adapted to generate a second counter signal by counting second compare signals;
a third comparator adapted to generate a motion signal by comparing the first counter signal to a predetermined third threshold;
a fourth comparator adapted to generate a no motion signal by comparing the second counter signal to a predetermined fourth threshold.
2. The deinterlace apparatus of
a field memory adapted to store the current and previous fields;
a line memory adapted to store predetermined lines of the future field.
3. The deinterlace apparatus of
4. The deinterlace apparatus of
5. The deinterlace apparatus of
a counter adapted to generate a count signal; and
a comparator adapted to generate a film mode signal by comparing the count signal to a predetermined threshold.
6. The deinterlace apparatus of
7. The deinterlace apparatus of
where the motion detector is adapted to generate motion, no motion, and film mode signals; and
where the switch is adapted to select between the spatially interpolated, temporal-spatially interpolated, and averaged output pixels responsive to the motion, no motion, and film mode signals.
9. The deinterlace apparatus of
10. The deinterlace apparatus of
a subtractor; and
an absolute operator.
12. The deinterlace apparatus of
a gradient calculation circuit adapted to calculate a gradient for each of a plurality of interpolation directions;
a minimum gradient determination circuit adapted to identify a minimum gradient direction from the gradients for each of the plurality of interpolation directions; and
an output pixel generator adapted to generate an output pixel responsive to the minimum gradient direction.
13. The deinterlace apparatus of
14. The deinterlace apparatus of
a gradient calculation circuit adapted to calculate a gradient for each of a plurality of interpolation directions;
a minimum gradient determination circuit adapted to identify a minimum gradient direction from the gradients for each of the plurality of interpolation directions; and
an output pixel generator adapted to generate an output pixel responsive to the minimum gradient direction.
15. The deinterlace apparatus of
17. The deinterlace method of
storing predetermined lines from the future field in a line memory;
storing the previous field sub image in a previous field memory; and
storing a current field sub image in a current field memory.
18. The deinterlace method of
taking an absolute difference between each pixel in the future field sub image and each pixel in the previous field sub image.
19. The deinterlace method of
calculating a plurality of gradients corresponding to a plurality of directions;
determining a minimum gradient direction from the plurality of gradients; and
spatially interpolating an output pixel responsive to the minimum gradient direction.
20. The deinterlace method of
21. The deinterlace method of
22. The deinterlace method of
calculating a plurality of gradients corresponding to a plurality of directions;
determining a minimum gradient direction from the plurality of gradients; and
spatial-temporally interpolating an output pixel responsive to the minimum gradient direction.
23. The deinterlace method of
selecting spatially interpolated pixels responsive to detecting motion;
selecting temporal-spatially interpolated pixels responsive to detecting no motion;
selecting averaged pixels responsive to the detecting motion;
selecting pixels from a previous field sub image responsive to detecting film mode.
26. The deinterlace method of
detecting a film mode by comparing each pixel in the future field sub image to each pixel in the previous field sub image.
27. The deinterlace method of
generating a third count by counting no motion signals; and
generating a film mode signal by comparing the third count to a film mode threshold.
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This application claims priority from and is a continuation of U.S. provisional patent application Ser. No. 60/366,721, filed Mar. 21, 2002. We incorporate all priority applications by reference.
1. Field of the Invention
The invention relates to a weighted absolute difference based deinterlace method and apparatus.
2. Description of the Related Art
The National Television Standards Committee (NTSC) is responsible for setting television video standards in the United States. The NTSC standard is interlaced. Each frame (480 viewable lines) is broken into two sections called fields (240 alternating viewable lines). A field containing even lines (0, 2, 4, . . . ) is termed an even field. Similarly, a field containing odd lines (1, 3, 5, . . . ) is termed an odd field.
Every 1/60 second, the NTSC standard requires displaying an even or an odd field. Because this process is happening quickly, the eye is tricked into seeing a full frame picture. The image quality resulting from the NTSC standard is acceptable on smaller television sets—those having roughly 27 inches viewable area. The image quality, however, quickly degrades as the screen size increases. This is because the NTSC standard creates artifacts, e.g., flickering, shimmering, and diagonal line jaggedness, visible to the eye on large screens. This image quality degradation renders the NTSC standard also unacceptable for high definition television (HDTV). And NTSC is incompatible with most personal computer and liquid crystal (LC) displays that operate on progressive scan. Progressive scan presents a higher quality alternative to the interlaced NTSC standard. Progressive scan require displaying alternating odd and even lines with each frame.
Accordingly, a need remains for an improved method and apparatus that converts interlaced to progressive scan signals.
The foregoing and other objects, features, and advantages of the invention will become more readily apparent from the detailed description of embodiments that reference the following drawings.
Converting interlaced video signals into progressively scanned video signals requires converting interlaced scanned fields, each comprising odd or even scan lines of a video signal frame, into progressively scanned fields, each comprising both odd and even scan lines.
The invention relates to a deinterlace method and apparatus adapted to interpolate pixel data for a missing line in an interlaced video signal. More particularly, the invention relates to a deinterlace method and apparatus using weighted absolute differences along different directions as means for interpolating pixel data using edge orientation detection.
The input luminance signal Yin passes to a first or current field memory 20 through 11. The current field memory 20 stores a current field of the input luminance signal Yin. The current field has a second polarity, e.g., odd.
The input luminance signal Yin passes to a second or previous field memory 30 through 21. The previous field memory 30 stores a previous field of the input luminance signal Yin. The previous field has a first polarity, e.g., even, same as the future field stored in the line memory 10.
The line memory 10 and the field memories 20 and 30 might be synchronous dynamic random access memory (SDRAM) or other types of memory. A person of reasonable skill in the art should recognize that the line memory 10 and the field memories 20 and 30 might be implemented in a singular memory, in distinct or separate memory, or any combination thereof.
Referring to
Referring to
Referring to
A person of reasonable skill in the art should recognize that any size of sub image comes within the scope of the present invention.
Referring to
The motion detector 200 detects motion between the future and previous field sub images 40 and 60. The motion detector 200 includes a subtractor 202 and an absolute operator 204. The subtractor 202 subtracts the luminance or value of a pixel in the future field sub image 42, e.g., pixel R34, from the luminance or value of a pixel in the previous field sub image 62, e.g., pixel Q34, where the pixels are located in the same position in the two different fields. That is, the subtractor 202 subtracts the future field sub image 42 from the previous field sub image 62 on a pixel-by-pixel basis through lines 41 and 63. The operator 204 takes the absolute of the difference produced by the subtractor 202 through line 203. The operator 204 provides the absolute difference to first and second comparators 210 and 220 through lines 207 and 205, respectively. The first comparator 210 compares the absolute difference at 207 to a first predetermined threshold 214. Likewise, the second comparator 220 compares the absolute difference at 205 to a second predetermined threshold 224. The first threshold 214 is typically set higher than the second threshold 224.
The first comparator 210 provides its results to a first counter 230 through line 211. The first counter 230 counts the number of cases where |Rij−Qij|>T214 in the sub image 42, where T214 is the first threshold 214. The first counter 230 provides its results to a third comparator 250. The third comparator asserts a motion signal at 251—indicating motion between future and previous sub images 40 and 60, respectively—when the results of the first counter 230 exceed a third threshold 254.
The second comparator 220 provides its results to a second counter 240 through line 221. The second counter 240 counts the number of cases where |Rij−Qij|<T224 in the sub image 42, T224 is the second threshold 224. The second counter 240 provides its results to a fourth comparator 260 through line 241. The fourth comparator 260 asserts a no motion signal at 263—indicating that the future and previous sub images 40 and 60, respectively, are part of a still (or non moving) portion of the video image—when the results of the second counter 240 exceed a fourth threshold 264.
The motion detector 200 includes a film mode detector 300 adapted to detect a film mode in the input luminance signal Yin. The film mode detector 300 comprises a film mode counter 270, comparator 280, and threshold 284. The film mode counter 270 counts the number of cases where the pixel to be interpolated x does not belong to a moving part of the image in a predetermined portion of the video image. The predetermined portion of the video image might be the whole field, the most active part of the video, an upper portion of the video, and the like. A person of reasonable skill in the art should understand that other criteria for selecting predetermined portions of the video image come within the scope of the present invention.
The film mode comparator 280 receives the counter 270's count at 271. The comparator 280 compares the count at 271 with the film mode threshold 284. The comparator 280 asserts a film mode signal at 281 if the count is less than the threshold 284. That is, the previous and the future fields come from the same frame indicating that the video was converted from film using the well known 3:2 pull down conversion method.
The first, second, third, fourth, and film mode thresholds 214, 224, 254, 264, 284, respectively, might be set through firmware, hardware, software, or a combination thereof.
The switch 100 selects output pixels at 71, 95, 81, 43, or 63 responsive to the motion signal at 251, the no motion signal at 263, and the film mode signal at 281. The switch 100 selects the spatially interpolated pixels at 71 responsive to the motion signal at 251. In this case, the correlation of the current field to the previous or future field is low. The effect of the previous or future field is, therefore, minimized. A purely spatial directional deinterlacing from the weighted absolute difference based spatial interpolator 70 is applied to interpolate the pixel of interest through 71.
The switch 100 selects the averaged signals at 95 responsive to the no motion signal at 263. The pixels at 95 are the average of R34 and Q34. Pixels from the future and previous sub image fields 42 and 62, respectively, are provided through line 45 and 61 to an adder 90.
The results of adder 90 are provided to a shift circuit 94 that outputs the average to line 95.
Put differently, a static mesh is applied to interpolate the pixel of interest x to increase the vertical resolution. Taking the average pixel value from the previous and future field sub images 40 and 60 allows about a 3 dB improvement in noise elimination.
The switch 100 selects spatial-temporally interpolated pixels at 81 responsive to the unasserted (or false) motion and no motion signals at 251 and 263, respectively. That is, if both the motion and no motion signals at 251 and 263 are false, the confidence that the pixel x to be interpolated belongs to either a moving or a still portion of the image is not high enough. The deinterlace apparatus, therefore, adopts a hybrid interpolation approach selecting spatial-temporally interpolated pixels at 81.
The switch 100 selects pixels at either 43 or 63 responsive to the film mode signal at 281, as we explain below. An asserted (or true) film mode signal at 281 will block the motion and no motion signals at 251 and 263, respectively, and thus, prevent the switch 100 from selecting the temporally interpolated, averaged, and spatial-temporally interpolated pixels at 71, 95, and 81, respectively. And an asserted film mode signal at 281 will disable the film mode detector 300 for four fields. For the next four fields, the deinterlace apparatus of
The lower circles represent the output frames. The number beside each circle represents the output frame count. The letters B or F below each lower circle represent the merge pattern. The letter B represents a backward merge that merges the current field with the previous field. The letter F represents a forward merge that mergers the current field with the future field. The two arrows toward each output frame represent that the frame comes from those two fields indicated by the two arrows. The input field pattern shown in
At the position of the output frame 0, the current, previous, and future fields are from frame 0 of the source film. The previous and future fields are theoretically identical. In practice, however, noise prevents the previous and future fields from being identical. The deinterlace apparatus detects identical fields by scanning only a portion (a sub image) of the field. In other words, in the deinterlace apparatus, it is unnecessary to scan the field in its entirety to determine whether the video originated from film. When the deinterlace apparatus detects identical fields, it immediately enters film mode. Before the apparatus completes its film mode detection, therefore, it calculates the missing lines of frame 0. Once in film mode, the apparatus fills the remaining missing lines of frame 0 by merging the corresponding lines in the future field. The result is a partially merged frame 0 that we represent in
The film mode detector 300 is disabled for the next four fields, corresponding to output frames 1, 2, 3, and 4. The deinterlace apparatus merges the current field with the previous field for output frames 1 and 3 and merges the current field with the future field for output frames 2 and 4. At the fifth field, which corresponds to output frame 5, the film mode detector is enabled, and the film mode signal remains asserted (true) until the count at 271 provided by counter 270 exceeds the threshold 284 again. If the count at 271 does not exceed the film mode threshold 284 for a predetermined region, the film mode detector 300 again detects identical future and previous fields, and the deinterlace apparatus again enters film mode for the next four fields. If the film mode detector 200 does not detect identical future and previous fields, the count at 271 soon—within just a few scan lines—exceeds the film mode threshold 284 and deasserts (false) the film mode signal at 281. The deasserted film mode signal at 281 immediately switches the deinterlace apparatus to video mode allowing the switch 100 to select spatially interpolated, averaged, and temporal-spatially interpolated pixels at 71, 95, and 81, respectively, responsive to the motion and no motions signals at 251 and 263, respectively. The video mode will prevent the switch 100 from merging output pixels from the future or previous fields at 43 and 67, respectively.
Referring back to
For example, at 706, the spatial interpolator 70 determines whether the minimum gradient Gmin is equal to the vertical gradient Gv. If it is, it calculates the output pixel Pout at 710.
If it is not, the spatial interpolator 70 determines whether the minimum gradient Gmin is equal to the horizontal gradient Gh at 716. If it is, it calculates the output pixel Pout at 720.
If it is not, the spatial interpolator 70 determines whether the minimum gradient Gmin is equal to the diagonal-1 gradient Gd1 at 726. If it is, it calculates the output pixel Pout at 730.
If it is not, the spatial interpolator 70 determines whether the minimum gradient Gmin is equal to the anti-diagonal-1 gradient Ga1 at 736. If it is, it calculates the output pixel Pout at 740.
If it is not, the spatial interpolator 70 determines whether the minimum gradient Gmin is equal to the diagonal gradient Gd at 746. If it is, it calculates the output pixel Pout at 750.
If it is not, the spatial interpolator 70 determines whether the minimum gradient Gmin is equal to the anti-diagonal gradient Ga at 756. If it is, it calculates the output pixel Pout at 760.
If it is not, the spatial interpolator 70 determines whether the minimum gradient Gmin is equal to the diagonal-2 gradient Gd2 at 766. If it is, it calculates the output pixel Pout at 770.
If it is not, the spatial interpolator 70 determines the minimum gradient Gmin is equal to the anti-diagonal-2 gradient Ga2 and calculates the output pixel Pout at 780.
When a line or edge passes through the pixel to be interpolated x (
The gradient is the derivative of a function on a given direction. In the digital domain, the derivative is replaced by a difference. The gradient is thus measured by differentiation of variously spaced pixels. For example, referring to
In one embodiment, the gradient is measured for the eight directions shown in FIG. 6. A person of skill in the art should recognize that other directions come within the scope of the present invention.
The gradient calculations for the eight directions are as follows.
Horizontal (H) direction
Gh=wh[a0(|P23−P24|+|P24−P25|+|P43−P44|+|P44−P45|)+a1(|P22−P23|+|P25−P26|+|P42−P43|+|P45−P46|)]
Vertical (V) direction
Gv=wv[b0|P24−P44 |+b1(|P23−P43|+|P25−P45|)+b2(|PO4−P24|+|P44−P46|)+b3(|PO3−P23|+|P43−P63|+|P05−P25|+|P45−P65|)]
Diagonal (D) direction
Gd=wd[c0|P23−P45|+c1(|P22−P44|+|P24−P46|)+c2(|P01−P23|+|P45−P67|+|P02−P24|+|P44−P66|)]
Anti-diagonal (A) direction
Ga=wd[c0|P25−P43|+c1(|P24−P42|+|P26−P44|)+C2(|PO7−P25|+|P43−P61|+|P06−P24|+|P44−P62|)]
Diagonal-1 (D1) direction
Gd1=wd1[d0(|P23−P44|+|P24−P45|)+d1(|P22−P43|+|P25−P46|)+d2(|PO3−P24|+|P44−P65|)+d3(|PO2−P23|+|P45−P66|)]
Anti-diagonal-1 (A1) direction
Ga1=wd1[d0(|P25−P44|+|P24−P43|)+d1(|P23−P42|+|P26−P45|)+d2(|PO5−P24|+|P44−P63|)+d3(|PO6−P25|+|P43−P62|)]
Diagonal-2 (D2) direction
Gd2=wd2[e0|P22−P46|+e1(|P21−P45|+|P23−P47|)+e2(|P00−P24|+|P24−P48|+|P20−44|+|P44−P68|)]
Anti-diagonal-2 (A2) direction
Ga2=wd2[e0|P26−P42|+e1(|P25−P41|+|P27−P43|)+e2(|PO8−P24|+P24−P40|+P28−P44|+|P44−P60|)]
In the gradient calculations, w's, a0, b0, c0, d0, and e0 are predetermined weights. The gradient for a plurality of directions, e.g., eight directions, will be calculated for the pixel to be interpolated x. The minimum gradient will give the interpolation direction.
We implement one embodiment of the spatial interpolator 70 as follows. We implement interpolation in the vertical, diagonal, and anti-diagonal directions using a four-tap low pass half-band filter. We implement interpolation in the diagonal-2 and anti-diagonal-2 directions using a two-tap low pass half-band filter. Horizontal interpolation is impossible since the horizontal line is entirely missing. Thus, we obtain the horizontal line by applying a low pass filter to the rows above and below and then averaging.
From simple geometry, the ratio of the lengths {overscore (P23A)} and {overscore (AP44)} is 3:2. That yields the formulas given in 730 and 740. An embodiment of the present invention, therefore, provides a mean of interpolation along D1 direction without requiring super-sampling. The interpolation method of the present invention is also more accurate than methods requiring super-sampling.
In one embodiment of the spatial-temporal interpolator 80, we use four directions, e.g., vertical, horizontal, diagonal, and anti-diagonal to interpolate the pixel x. A person of reasonable skill in the art should understand directions other than those mentioned can be used instead of or in conjunction with those we mention above, and that all combinations thereof come within the scope of the invention.
Referring to
The spatial-temporal interpolator 80 determines the minimum gradient Gmin at 804.
The spatial-temporal interpolator 80 then compares each of the four gradients Gv, Gh, Gd, and Ga, against the minimum gradient Gmin.
For example, at 806, the spatial-temporal interpolator 80 determines whether the minimum gradient Gmin is equal to the vertical gradient Gv. If it is, it calculates the output pixel Pout at 810.
If it is not, the spatial-temporal interpolator 80 determines whether the minimum gradient Gmin is equal to the horizontal gradient Gh at 816. If it is, it calculates the output pixel Pout at 820.
If it is not, the spatial-temporal interpolator 80 determines whether the minimum gradient Gmin is equal to the diagonal gradient Gd at 826. If it is, it calculates the output pixel Pout at 830.
If it is not, the spatial-temporal interpolator 80 determines the minimum gradient Gmin is equal to the anti-diagonal gradient Ga and calculates the output pixel Pout at 840.
We implement one embodiment of the spatial-temporal interpolator 80 as follows. We implement interpolation in the vertical, diagonal, and anti-diagonal directions using a seven-tap spatial-temporal filter. We obtain the horizontal line by averaging the still and moving image portions.
It should be readily apparent that the deinterlace method and apparatus might be implemented using hardware, software, firmware, or a combination thereof. The deinterlace method and apparatus might include a microprocessor or a microcontroller. And the deinterlace apparatus and method might be specially constructed for the required purposes or it might comprise a general-purpose computer selectively activated or reconfigured by a computer program stored in the computer.
We have described and illustrated the principles of our invention. Those of skill in the art should recognize that the invention might be modified in arrangement and detail without departing from these principles. We claim all modifications coming within the spirit and scope of the accompanying claims.
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